The present invention relates to improvement in electrical insulation of electrodes called stem pins, provided for supplying/receiving electric signals, of a cathode-ray tube.
With the tendency to increase a voltage applied to stem pins of an electron gun for improving the performance of a color cathode-ray tube, a stem portion of the cathode-ray tube has been insulated by coating the stem portion with a room temperature curing type silicon resin. The room temperature curing type silicon resin, however, is disadvantageous in that it entraps bubbles when being cured. To solve degradation of insulation due to the bubbles, an electrical insulator used for insulation of a stem portion of a cathode-ray tube, and a cathode-ray tube provided with the electrical insulator for improving the insulation of a stem portion have been disclosed in Japanese Patent Laid-open Nos. Hei 7-94100 and Hei 8-111191.
According to the invention disclosed in Japanese Patent Laid-open No. Hei 7-94100, a cathode-ray tube with the improved insulation is manufactured by a manner of preparing a flat electrical insulator made from a silicon compound, punching the electrical insulator with a forming die to form holes in which stem pins and a stem tip are to be inserted, sticking the electrical insulator on a stem base, mounting the stem base thus stuck with the electrical insulator on a stem of the cathode-ray tube, and heating the cathode-ray tube to ensure the adhesive strength of the electrical insulator to the stem base.
According to the invention disclosed in Japanese Patent Laid-open No. Hei 8-111191, a cathode-ray tube is manufactured by a manner of extruding a thermosetting adhesive type silicon rubber composition into a tape, punching the tape into a half-cut shape using a die set to form holes in which stem pins required to be insulated when high voltages are applied thereto and a stem tip are to be inserted, sticking the electrical insulator tape on a stem base in such a manner as to be caught between a tip containing portion of the stem base and the stem tip, and mounting the stem base thus stuck with the electrical insulator tape on a stem of the cathode-ray tube, thereby improving the insulation between the stem pins to which high voltages are applied.
In the inventions disclosed in Japanese Patent Laid-open Nos. Hei 7-94100 and Hei 8-111191, the electrical insulator formed into the flat or tape shape is punched using a forming die or die set, and accordingly a surface to be brought into contact with the stem of the electrical insulator is formed into a smooth plane.
As a result, in both the inventions, when the stem base stuck with the electrical insulator is mounted on the stem, air may be entrapped between the smooth surface of the electrical insulator and the surface of the stem, and if gaps formed by the entrapped air are present between the stem pins required to be insulated, there may occur a problem in generating discharge due to degradation of insulation of the stem portion of the cathode-ray tube.